1. Field of the Invention
The present invention relates to a scanning probe microscope and a scanning method for obtaining physical property information, such as surface shape, of a sample by scanning a probe needle while being vibrated on a sample surface.
2. Description of the Related Art
As well known, as an apparatus for performing an observation of the surface shape of the sample and a measurement of the physical properties information by measuring the sample such as electronic material in a minute region, there is used the scanning probe microscope such as atomic force microscope (AFM) and scanning tunnel microscope (STM). In the scanning probe microscope of this kind, although there are provided various ones, as one of them there is known a vibration mode (AC mode) AFM which detects the surface shape and the like of the sample by scanning the probe needle parallel to the sample surface while being vibrated perpendicularly to the sample surface. In the vibration mode AFM, there are a system in which the probe needle is scanned so as not to contact with the sample surface under a state that the probe needle has been approached to the sample surface, and a system in which it is scanned while repeatedly beating the sample surface. (For example, refer to Patent Document 1.)
This vibration mode AFM possesses the probe needle attached to a tip of a cantilever. And, this probe needle is adapted so as to be capable of scanning with respect to the sample surface, and adapted so as to be capable of vibrating at a resonance frequency of the cantilever or its vicinity. In a case where the surface shape of the sample is measured by this vibration mode AFM, the probe needle is vibrated as mentioned above, and the probe needle and the sample surface are relatively approached. Since a force such as van der Waals force and repulsive force by a contact acts between the probe needle and the sample surface, a vibration state of the probe needle changes. Whereupon, when the probe needle has changed till a certain vibration state, it is judged that the probe needle and the sample surface have approached or contacted, and a measurement of the surface shape of the sample is performed by scanning the probe needle with respect to the sample surface while adjusting a distance between the probe needle and the sample surface so as to maintain the above vibration state.
[Patent Document 1] JP-A-7-270434 Gazette
However, in the above conventional scanning probe microscope, there are following problems. That is, in the above conventional scanning probe microscope, when there are irregularities in the sample surface, even if a distance between the probe needle and the sample surface in an observation position is made equal, since a difference in influence on the probe needle by the fact that the irregularities of the sample surface differ or a distance between the cantilever and the sample surface is changed by the irregularities of the sample surface, a different vibration state is shown. Although this vibrates the probe needle by the fact that the cantilever resonates or forcibly vibrates, since a ratio of a space compressed by this resonance or forcible vibration of the cantilever to a space between the cantilever and the sample surface changes by the irregularities of the sample surface, it follows that a damping effect (resisting effect) given to the cantilever differs. By this, it follows that the probe needle shows the different vibration state, and there is a problem that, even if the probe needle is scanned with respect to the sample surface by adjusting the distance between the probe needle an d the sample surface so as to maintain a certain vibration state, the distance between the probe needle and the sample surface does not become constant. Accordingly, there is a problem that probe needle and the sample surface cannot be accurately approached or contacted.